This invention relates to a scanner, particularly to a scanner module with adjustable optical distance and magnification ratio. The scanner module includes a pressing device (such as a wedge element or an adjusting screw) and a fastening spring for adjusting (lengthening or shortening) the total optical distance from a document to the charge-coupled device module, thus reducing the tolerance of the magnification ratio.
FIG. 1 (Prior Art) is a diagram illustrating basic operations of a scanner module, wherein an object 1 to be scanned (such as a document or a picture) is focused and imaged at a charge-coupled device 3 through a lens 2. The distance between the center of the lens 2 and the object 1 is called an object distance p; and the distance between the center of the lens 2 and the charge-coupled device 3 is called an image distance q. The magnification ratio between the object 1 and the image is defined as the ratio of the image distance q to the object distance q.       magnification    ⁢          xe2x80x83        ⁢    ratio    =            image      object        =          q      p      
In a scanner module, the object distance p is normally longer than the image distance q. Therefore, the total optical distance is ordinarily lengthened by virtue of reflective mirrors to minimize the space the scanner module occupies, as shown in FIG. 2 (Prior Art) . In this case, the object distance p between the center of the lens 2 and the object 1 can be treated as the sum of all the reflective paths passing through the four mirrors M, M2, M3 and M4, that is: p=p1+p2+p3+p4+p5. Therefore, the optical distance may vary due to variation in angles of the mirrors M1, M2, M3, and M4 and affect the magnification ratio and MTF value of the scanner module. In addition, the change in shape of the photo-mechanical body and the casing (not shown in the figure) may also result in difference of the optical distance and increase the tolerance of the magnification ratio. Assume the tolerance of the magnification ratio of the lens 2 is approximately xc2x11%, taking into account the difference of the optical distance (OD), the tolerance of the entire magnification ratio of the scanner module can reach from 1.5% to 2%. Hence, the image quality may be significantly affected.
However, current scanner modules fail to improve the magnification ratio substantially. As a result, the required tolerance of the magnification ratio (such as 0.5%) of the lens 2 must be reduced to render better image quality. Unfortunately, this will also reduce the yield of the lens and the entire magnification ratio of the scanner module is also higher than the tolerance of the lens 2.
Accordingly, it is an object of this invention is to provide a scanner module with adjustable optical distance and adjustable magnification ratio, wherein the tolerance of the scanner module can be reduced (even lower than the tolerance of magnification ratio of a single lens) to substantially enhance the picture quality.
It is another object of this invention is to provide a scanner module with adjustable magnification ratio, wherein a support plane is formed on the photo-mechanical body to push the charge-coupled device module to move back and forth along the direction of the optical distance, and to extend or shorten the total optical distance (object distance p plus image distance q) of the scanner module. When the total length of the optical distance of the scanner module changes, the magnification ratio of the scanner module can be also adjusted to the optimum.
To achieve the above objects, this invention provides a scanner module with adjustable magnification ratio. The scanner module includes a photo-mechanical body, a charge-coupled device module and a pressing device, such as a wedge element or an adjusting screw. The photo-mechanical body is arranged along an optical distance and has a first plane vertical to the direction of the optical distance. The charge-coupled device module is arranged along the direction of the optical distance in the photo-mechanical body and has a second plane vertical to the optical distance and facing to the first plane. The pressing device is supported by the second plane and vertical to the first plane, for enabling the charge-coupled device module to move back and forth along the optical distance. Therefore, the magnification ratio of the scanner module can be adjusted through the length of the optical distance. In addition, a cylinder or guiding slot can also be arranged at the sides of the charge-coupled device module in the photo-mechanical body, for positioning the charge-coupled device module when the photo-mechanical body is moving.